Space is full of a lot of... err... empty space.
This means that you can find ways to compress the 'decision space' down into much smaller units. In addition to solar system zones, you could implement something like sparse arrays (hashing) or an octtree (binary space partition) to ignore much of the empty bits and focus on the actual objects in each zone.
This will be less effective if you have some sort of sensors that give a 'radar' reading of where all ships are within the zone - but at least you would avoid having to consider laser fire, etc. for events offscreen.
This means that you can find ways to compress the 'decision space' down into much smaller units. In addition to solar system zones, you could implement something like sparse arrays (hashing) or an octtree (binary space partition) to ignore much of the empty bits and focus on the actual objects in each zone.
This will be less effective if you have some sort of sensors that give a 'radar' reading of where all ships are within the zone - but at least you would avoid having to consider laser fire, etc. for events offscreen.